Hydraulic drive



l Nov. 27, 1945.

R. TYLER 2,389,830

HYDRAULIC DRIVE Filed Aug. 15, 1942 ATTORNEY.

atented Nov. 27, 1945 HYDRAULIC DRIVE Ransom Tyler, Greenfield, Wis., assigner to The Gilgear Company, Milwaukee, Wis., a corporation o? Wisconsin Application August l5, 1942, Serial No. 454,982

(Cl. Gil-53) 13 claims.

This invention relates to hydraulic drives of the type employed to drive a plurality of shafts or machine elements the speeds of which should be maintained at an exact ratio. i

Various drives of this type have heretofore been provided some of which function satisfactorily when the drive is operating at or near its normal speed but which fail to maintain the desired ratio between the speeds of the shaft or elements during starting and stopping of the drive.

The primary object of the presentl invention is to provide a hydraulic drive capable of driving a plurality of shafts or elements at a desired ratio and maintaining that ratio substantially constant throughout the entire range of speeds between zero and maximum.

Other objects and advantages will appear from the following description of a drive constructed according to the invention and shown schematically in the accompanying drawing in which the views are as follows:

Fig. l is a circuit diagram of 4a drive embodying the invention. g

Fig. 2 is a view showing the start and stop valve in a position different from that shown in Fig. 1.

For the purpose of illustration, the invention has been shown embodied in a drive adapted to drive, for example, a wire forming machine of which, since it forms no part of the present invention, only the drive shaft i oi' the feeding section and the drive shaft 2 of the forming section have been shown. The feeding section feeds a continuous strand or lstrands of wire to the forming section which c1"'s the wire intopieces of equal length and foris the pieces into articles of desired shapes. Tinspeeds of the two sections must be kept proportional to each other as otherwise the pieces cut from the wire would vary in length and be too long or too short to form iinished articles of the desired shapes.

Shaft I is driven by a hydraulic transmission comprising' a motor 3 and a pump ll, and shaft 2 is driven by a hydraulic transmission comprising a motor and a pump 6. Motor 3 has its shaft 7 mechanically connected to shaft l, as by means of a coupling s, and it is hydraulically connected to Y pump ,il by channels 9 and iii. Motor thas its shaft I I mechanically connected to shaft 2, as by means of e, coupling I2, and it is hydraulically connected to pump E by channels I3 and I. Each of the pumps is driven at a substantially constant speed by power derived from a suitable power source such as an electric motor not shown.

t Pump 5 may be of any suitable type but it has described in Patent No. 2,074,068. it 1s deemed suicient to state herein that its pumping mechanism is arranged within a displacement varying member or slide block 'I5 and that it will deliver liquid to motor 5 at a rate determined by the distance slide block I5 is offset from its neutral position, the displacement and delivery of pump 6 being zero when slide block I5 is in neutral position.. I

Slide block I5 is constantly urged toward neutral position by low pressure liquid acting upon a servo-motor piston I6 which is connected to or abuts slide block I5 and is tted in a cylinder I1 :fixed to the casing of pump 5. Slide block I5 is adapted to be moved toward the right away from its neutral position by liquid at a higher pressure acting upon a servo-motor piston I8 which is connected to or abuts slideblock I5 and is fitted in a i cylinder I9 iixed to the casing of pump 6.

Pump li may be of the same general construction as pump 6 and it is preferably of the variable displacement type. As shown, its slide block 20 is adapted to be shifted by a manually operable screw 2i which may be rotated to vary the displacement of pump Il and thereby vary the overall speed of the machine. Motors 3 and 5 may be of the same general construction as pump 6 but they are ordinarily of the constant displacement type.

Motor 5 is started and stopped by shifting slide block I5 of pump 6 from and to its neutral position. Motor 3 is started and stopped by means of a valve 25 arrangedin a valve casing 26 which is connected intermediate its ends by channels 21 and 28 to opposite sides of pump 4 and has its ends connected to drain as by being connected to a reservoir 29 arranged beneath the casing of pump 4. Valve 25 controls communication between channels 21 and 28 and between channel 2l and a channel 30 into which liquid from pump 4 is directed for a purpose to be presently explained.

Liquid for energizing servo-motor IG-Il may be supplied thereto from any suitable low pressure source such asa gear pump 3| which has been shown separate from pump 4 but which in practice is driven in unison with pump 4 and arranged in the casing thereof in the customarymanner and as shown in Patent 2,074,068. Gear pump 3|' draws liquid from reservoir 29 and discharges it into a channel 32 which is connected to cylinder Il. The liquid discharged by gear pump 3| in excess of requirements is exhausted into reservoir 29 through a low pressure relief valve 33 which enables gear pump 3| to maintain been shown as being of the type illustrated and in channel 32 and in cylinder I'I a constant low pressureproportional to the resistance of relief valve 33.

Liquid for energizing servo-motor I8I3 when the machine is running is supplied thereto in response to a variation in the relative speeds of two small pumps or meters 36 and 31 which are driven in synchronism with motors 3 and 5 respectively. As shown, meter 36 has its shaft connected to the shaft 1 of motor 3 by a drive 33 and meter 31 has its shaft connected to the shaft I I of motor by a drive 39.A

Meters 33 and 31 are connected together into a closed circuit by means of a channel 40, which connects the inlet of meter 36 to the outlet of meter 31, and a channel 4I which connects the outlet of meter -36 to .the inlet of meter 31 and which is also connected by a channel 42 to cylinder I9. In order'to keep the circuit completely filled with liquid, channel 40 is connected to. gear pump channel 32 by a channel 43 and channel 4| is connected to gear pump channel 32 by a channel 44 having arranged therein a check valve 45 which permits liquid to flow from channel 3'2 into channel 4I but prevents liquid from ilowing from channel 4I into channel 32.

The function of meters 36 and 31 is to maintain the speed of motor 5 proportional to the speed of motor 3. 'Ihe ratio between the speeds of motors 3 and 5 is determined by the relative displacements of meters 36 and 31 and by the speeds at which the meters are driven.

In order that the ratio between the speeds of motors 3 and 5 may be readily varied, one or both of the motors may be provided with means for varying its displacement. As shown, meter 36 is provided with a hand wheel 46 for varying its displacement. For example, meter 36 may be of the same type as pump 4 and have its displacement varied in substantially the vsame manner.

Meters 36 and 31 are capable of maintaining the speed of motor 5 proportional to the speed of motor 3 during normal operation of the drive but they are incapable of causing motor 5 to start simultaneously with motor 3 or to decelerate to a stop synchronously with motor 3.

In order that motor 5 may be started and stopped synchronously with motor 3, a metered volume of liquid is supplied to or permitted to escape from cylinder I9 in response to operation of start and stop valve 25. This is accomplished by means of a metering device comprising a cylinder 5| and a piston 52 tted therein. The device may also include an adjusting screw 53 for limiting the stroke of piston 52 to thereby regulate the volume of liquid supplied to or permitted to escape from cylinder I9.

Cylinder 5I has channel 30 connected to one of its ends and a channel 54 connected to its other end. Channel 54 is connected to channel 42 through two oppositely opening check valves 55 and 56, which are arranged in parallel with each other, a throttle valve 51 which is connected in series with check valve 55 and a throttle valve 56 which is connected in series with check valve 56.

Operiation With the parts in the positions shown and the pumps running, the liquid discharged by pump 4 flows through channel 21, valve casing 26 and channel 23 back to the intake of pump 4 so that motor 3 is idle, gear pump 3l is drawing liquid from reservoir 29 and discharging it through relief valve 33 back into reservoir 29. The pressure created by gear pump 3l extends through channels 32 and 42 and acts upon pistons I6 and I3. Since piston I3 is larger than piston I3, it holds lpump 6 at zero stroke so that motor 5 is idle. Gear pump pressure also extends from channel 42 through valves 53 and 56 and channel 54 to cylinder 5I and holds piston 52 against the left end of cylinder 5| as shown.

When valve 25 is shifted from the position shown in Fig. 1 to the position shown in Fig. 2, liquid discharged by pump 4 will flow through channel 9 to motor 3 to energize it and at the same time liquid will ilowr from pump 4 through channel 21, valve casing 26 and channel 30 to cylinder 5| and cause piston 52 to move toward the right and expel a predetermined volume of liquid from cylinder 5I through channel 54, check valve 55 and throttle valve 51 into channel 42 and cylinder I9,

Since this predetermined volume of liquid cannot escape from channel 42 into the gear pump circuit due to check valve 45 and since piston I8 is being held in its zero displacement position by gear pump pressure acting upon piston I6 the area of which is somewhat larger than the area of piston I6, piston 52 will create in channel 42 and in cylinder I9 a pressure of a low value but enough higher` than gear pump pressure to enable piston I8 to shift slide block I5 toward the right to cause pump 6 to deliver liquid through channel I3 to motor 5 to energize it. Motors 3 and 5 are thus started simultaneously.

The volume of liquid expelled from cylinder 5| into cylinder I9 is just suflicient to enable piston I8 to shift slide block I5 far enough to enable pump 6 to discharge liquid at the rate required to drive motor 5 at a predetermined speed such as its normal running speed. If the ow from cylinder 5I to cylinder I9 were unrestricted, the volumetric delivery of pump l would be almost instantly increased to the predetermined value and motor 5 would be accelerated at an uncontrolled rate which might be too great to maintain the speeds of motors 3 and f 5 at the preset ratio but the flow to cylinder I9 is restricted by throttle valve 51 which may be adjusted to regulate the rate at which the displacement of pump 6 is increased and thereby regulate the rate at which motor 5 is accelerated.

As soon as motors 3 and 5 start to operate. meters 36 and 31 start to operate in unison therewith respectively. If motor 5 and meter 31 should run too slow relative tothe speeds of motor 3 and meter 36 or ifvthe speed of meter 36 should be increased as by increasing the displacement of pump 4, and thereby increasing the speed of motor 3, the volume of liquid discharged by meter 36 into channel 4| would be in excess of the volume drawn therefrom by meter 3'1 and the excess liquid would flow through channel 42 to cylinder I3 and cause piston I3 to increase the displacement of pump 6 and thereby increase the speeds of motor 5 and meter 31 until the speeds of motors 3 and 5 were at the preset ratio and then the intake rate of meter 31 would exactly equal the output rate of meter 36 and further adjustment of pump 6 would cease.

If the speed of motor 5 should increase relative to the speed of motor 3 or if the speed of motor 3 into reservoir 29. The volume of liquid disto meter 31. The liquid drawn from cylinder I9 by meter 31 would enable the gear pump pressure in cylinder il to cause piston I6 to move -slide block I5 toward the left to decrease the speeds of motor 5 and meter 31 until the speeds of motors 3 and 5 were at the preset ratio and then the intake rate of meter 31 would exactly equal the output rate of lmeter 36 and further adjustment of pump 6 would cease.

When valve 25 is shifted to the position shown in Fig. l to bypass pump 4 as previously explained, motor 5 will coast to a stop. Shifting valve 25 will also connect channel 30 to drain and enable the liquid supplied to cylinder I1 by gear pump 3i to cause piston i6 to shift slide block I5 toward the left and the liquid expelled from cylinder i9 by piston I8 during movement of slide block i5 toward the left will flow through channel 42, throttle valve 58, check valve 56 and channel 54 to cylinder 5I and move piston 52 toward its neutral position.

If the flow from cylinder I9 were unrestricted,

the displacement of pump 6 would be reduced to zero almost instantly and the liquid discharged by motor 5 would be forced through the-high pressure relief valve of pump 6, thereby imposing a high brake load upon motor 5 and causing it to decelerate faster than motor 3. However, throttle valve 58 is adjusted to so regulate the rate of discharge from cylinder I9 that the rate of deceleration of motor 5 is maintained proportional to the rate of deceleration of motor 3, meters 36 and 31 continuing to control at least in part the speed of motor 5 relative to the speed of motor 3 during deceleration of the motors.

f when valve 25 is shifted slide block I5 is located at or toward the left from the position to which it was initially moved in response to operation of piston 52, it will be returned to neutral in response to operation of valve 25 but if at that time it is located at the right of lthat position, operation of valve 25 will cause piston I6 to move slide block I5 toward the left until the liquid ejected from cylinder I9 by piston I8 has fully retracted piston 52 and thereafter piston i6 will move slide block I5 farther toward the left to its neutral position in response to meter 31 drawing liquid from cylinder i9 due to meter 36 decelerating faster than meter 31.

If the volume of liquid delivered to cylinder 5I from cylinder I9 is insufficient to move piston 52 fully to its initial position, liquid from gear pump 3i will flow through channel 32, check valve 45, channels M, di and 42, throttle valve 58, check valve 56 and channel 54 to cylinder 5I and move piston 52 fully to its initial position.

While the invention has been shown embodied in a drive comprising a master transmission for driving one shaft or machine, a follower transmission for driving a second shaft or machine and controls for maintaining the speeds of the shafts or machines at a given ratio, it will be obvious that the invention may be adapted to drive a larger number of shafts or machines by simply adding additional follower transmission and controls therefor and that the drive is susceptible of variousl other modifications and adaptations without departing from the scope of the invention which is hereby claimed as follows:

l. In a hydraulic drive having a rst hydraulic motor, a rst pump connected to said motor to energize the same, a second hydraulic motor, a second pump connected to said second motor to energize the same and provided with a hydraulically operated control for varying its displacement, the combination of means responsive to a variation in the relative speeds of said motors for effecting operation of said pump control to thereby correct suchspeed variation, means for starting said first motor, and means independent of said speed responsive means and responsive to operation of said starting means for effecting operation of said pump control to thereby cause said second motor to start substantially simultaneously with said first motor.

2. In a hydraulic drive having a first hydraulic motor, a first pump connected to said motor to energize the same, a second hydraulic motor, a second pump connected to said second motor to energize the same and provided with a hydraulically operated control for varying its displacement, the combination of means for controlling the flow of liquid from said rst pump to said rst motor, and means for causing a predetermined quantity of liquid to flow to said pump control and thereby effect a definite adjustment of the displacement of said second pump in response to operation of said flow control means.

3. In a hydraulic drive having a first hydraulic motor, a first pump connected to said motor to energize the same, a' second hydraulic motor, a second pump connected to said second motorl to energize the same and .provided with a hydraulically operated control for varying its dis.. placement, the combination of means for controlling the flow of liquid from said first pump to said first motor, means responsive to operation motor, a second pump connected to saidv second motor to energize the same and provided with a hydraulically operated control for varying its displacement, the combination of means for controlling the flow of liquid from said lrst pump to said first motor, means responsive to oper` ation of said flow control means for causing a denite volume of liquid to flow to or from said pump control and thereby effect a variation in the displacement of said second pump, and two oppositelyl opening check Ivalves connected between said last mentioned means and said pump control in parallel with each other and a choke connected in series with each check valve to regulate the rate at which said definite volume of liquid may flow to or from said pump control.

5. In a hydraulic drive having a rst hydraulic motor, a'lrst pump connected to said motor to enengize the same, a second hydraulic motor, a second pump conneced to said second motor to energize the same and provided with a' hy-l trolling said first motor-and said metering device to effect simultaneous operation thereof.

6. In a hydraulic drive having a iirsthydraulic motor, a first pump connected to said motor to energize the same, a second hydraulic motor;` a second pump connected to said second motor to energize the same and provided with a hydraulically operated control for varying its displacement. the combination of means responsive to a variation in the relative speeds of said motors for effecting operation of said pump control to thereby correct such speed variation, a metering device for directing a definite volume of liquid to and for receiving saiddefinite volume of liquid -fron said pump control, a valve for controlling said first motor and said metering device to Aeiiect simultaneous operation thereof, and means for regulatingr the rate of flow of said definite volume of liquid in each direction independently of its rate of flow in the opposite direction.

'7. In a hydraulic drive having a first hydraulic motor, a first pump connected to said motor to energize the same, a second hydraulic motor, a second pump connected to said second motor to energize the same and provided with a hydraulically operated control for varying its displacement, the combination of a valve for controlling the flow of liquid from said first pump to said first motor, a cylinder having one end connected to said pump control and its other end connected to said valve, and a piston in said cylinder adapted when energized to eject a definite volume of liquid from said cylinder to said pump control, said valve being shiftable to two positions in one of which it causes liquid to flow from said first pump to said first motor and to said cylinder and in the other of which it bypasses said first pump and connects said cylinder to exhaust.

8. In a hydraulic drive having a iirst hydraulic second pump connected to said second motor to l unison with each of said motors, fluid channels connecting said meters to each other and forming therewith a closed hydraulic circuit completely filled with liquid, a channel connecting one side of said circuit to said pump control so that a variation in the relative speeds of said' meters will effect a ilow of liquid to or from said pump control and cause the same to vary the displacement oi said second pump, means for starting said first motor, and additional means responsive t'o operation of said starting means for effecting operation of said pump control to thereby cause said second motor to start substantially simultaneously with said first motor.

10. In a hydraulic drive having a first hydraulic motor, a first pump connected to said motor to l energize the same, a second hydraulic motor, a

second pump connected to said second motor to energize the same and provided with a hydraulically operated control lfor varying its displacement, the combination of a fluid meter driven in unison with each of said motors, fluid channels connecting said meters to each other and forming therewith a closed hydraulic circuit completely iilled with liquid, a channel connecting one side of said circuit to said pump control so that a variation in the relative speeds of said meters will effect a flow of liquid to or from said pump control and cause the same to vary the displacement of said second pump, means for controlling the flow of liquid from said first pump to said iirst motor, additional means responsive to operation of said flow control means iorvcausing a definite volume of liquid to flow to or from said pump control and thereby effect a variation 0 in the displacement of said second pump, and

motor, a iirst pump connected to said motor to energize the same, a second hydraulic motor,

a second pump connected to said second motor 4to energize the same and provided with a hydraulically operated control for varying vits displacement, the combination of a valve for controlling the flow of liquid from said first pump to said rst motor, a cylinder having a iirst end thereof connected to said pump control and the second end thereof connected to said valve, a piston in said cylinder adapted when energized to eject a definite volume of liquid from said cylinder to said pump control, said valve being shiftable to two positions in one of which it causes liquid to flow from said first pump to said first motor and to the second end of said cylinder and in the other of which it bypasses said first pump and connects the second end of said cylinder to exhaust, and means for supplying liquid to the rst end of said cylinder to completely fill the same and to urge said piston against the second end of said cylinder during the time said piston is deenergized.

. 9. In a hydraulic drive having a rst hydraulic motor, a rst pump connected to said motor to means for regulating the rate of now of said definite volume of liquid to thereby regulate the rate at which the displacement of said second pump is varied.

1l. In a hydraulic drive having a first hydraulic motor, a rst pump connected to said motor to energize the same, a second hydraulic motor, a second pump connected to said second motor to energize the same and provided with a hydraulically operated control for varying its displacement, the combination of a iiuid meter driven in unison with each of said motors, iiuid channels connecting said meters to each other and forming therewith a closed hydraulic circuit completely iilled with liquid, a channel connecting one side of said circuit to said pump control so that a variation in the relative speeds of said meters will effect a ilow of liquid to or from said pump control and cause the same to vary the displacement of said second pump, a metering device for directing a definite volume of liquid to and for receiving said definite volume of liquid from said pump control, and a valve for controlling said iirst motor and said metering device to effect simultaneousoperation thereof.

12. In a hydraulic drive having a first hydraulic motor, a first pump connected to said motor to energize the same, a second hydraulic motor. a second pump connected to said second motor to energize the same and provided with a hydraulically operated control for varying its displacement, the combination of a iiuid meter driven in unison with each of said motors, fluid channels connecting said meters to each other energize the same, a second hydraulic motor, a 'Il and forming therewith a closed hydraulic circuit completely lled with liquid, a channel connectl ing one side of said circuit to said pump control so that a variation in the relative speeds oi said meters will effect a flow of liquid to or from said pump control and cause the same to vary the displacement of said second pump, a metering device for directing a deinite volume of liquid to and for receiving said deilnite volume of liquid from said pump control, a valve for controlling said iirst motor and said metering device to effect simultaneous operation thereof,`and means for regulating the rate of ow of said deilnite volume of liquid in each direction independently of its ing one side of said circuit to'said pump control so that a variation in the relative speeds of said meters will eiect a ilow oi liquid to or from said pump control and cause the same to vary the displacement of said second pump, a. valve for controlling the ilow of liquid from said first pump 'to said first motor, a. cylinder having a nrst end thereof connected to Asaid pump control and the second end thereof connected to said valve, a piston in said cylinder adapted when energized to eject a definite volume of liquid from said cylinder to said pump control, said valve -being shiftable to two positions in one of which it causes liquid to ow from said first pump to said rst motor and to the second end of said cylinder an'd in the other of which it bypasses said first pump and connects the second end of said cylinder to exhaust, and means for supplying' liquid to the first end of said cylinder to completely ll the same and t0 urge said piston against the second end oi' said cylinder during the time said piston is deenergized.

RANSOM TYLER. 

